In automotive vehicles having automatic transmissions it is common practice to provide a heat exchanger for transmission oil to regulate the internal temperature of the transmission. Often the heat exchanger, called an oil cooler, is combined with the vehicle radiator which cools the vehicle engine by transferring heat from the engine coolant to the ambient air. Such radiators comprise an array of heat exchange tubes arranged in parallel between two headers which hold the tubes in place, and a tank secured to each header to provide respective inlet and outlet reservoirs. Hot coolant from the engine is circulated to the inlet tank, through the heat exchange tubes to the outlet tank, and the cooler coolant is then returned to the engine. Cooling of the transmission oil is accomplished by placing the oil cooler in the outlet tank for heat transfer to the coolant.
One type of oil cooler is a double walled tube immersed in the engine coolant so that the coolant will flow along the outside and inside surfaces for heat transfer from hot oil which is circulated between the tube walls. Typically, the cooler is mounted in the outlet tank so that coolant flows from the heat exchange tubes onto the outer surface of the cooler and some of the coolant passes through the center passage of the cooler and the rest flows directly to the tank outlet, bypassing the center passage of the cooler. To obtain adequate oil cooling for a given size of tank and oil cooler, it is desirable to optimize the heat transfer efficiency of an oil cooler in a radiator tank. It has been found that efficiency of the oil cooler can be enhanced by improving the coolant flow in the tank.